POJ-1915 Knight Moves (BFS)

#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;

const int MAX=305;
int l,sx,sy,ex,ey;
int dx[8]={-2,-2,-1,-1,1,1,2,2};
int dy[8]={1,-1,2,-2,2,-2,1,-1};
bool vis[MAX][MAX];
struct Node
{
    int x,y,step;
    bool operator < (const Node &a) const{
        return a.step<step;
    }
};
priority_queue<Node> q;//利用优先队列，每次出队的为步数较小的。

void bfs()
{
    Node now,next;
    now.x=sx; now.y=sy; now.step=0;
    while(!q.empty())    //由于多组数据，每次bfs都要清空q
    {
        q.pop();
    }
    q.push(now);
    while(!q.empty())
    {
        now = q.top();
        q.pop();
        if(now.x==ex&&now.y==ey) //bfs结束，找到出口
        {
            printf("%d\n",now.step);
            break;
        }
        for(int i=0;i<8;i++)
        {
            next.x = now.x+dx[i];
            next.y = now.y+dy[i];
            if(next.x>=0&&next.x<l &&next.y>=0&&next.y<l && !vis[next.x][next.y])
            {
                vis[next.x][next.y]=true;
                next.step = now.step+1;
                q.push(next);
            }
        }
    }
}

int main()
{
    int Case;
    scanf("%d",&Case);
    while(Case--)
    {
        memset(vis,false,sizeof(vis));
        scanf("%d",&l);
        scanf("%d %d",&sx,&sy);
        scanf("%d %d",&ex,&ey);
        bfs();
        //printf("bfs-end\n");
    }
}